Chelsea were in negotiations with Porto last night to sign Joao Moutinho and Alvaro Pereira.

A bid of between £18m and £22m is set to be made for Uruguay international Pereira -- who is the most likely arrival -- while Chelsea are prepared to offer £26m for Moutinho, a favourite of manager Andre Villas-Boas, who left the Portuguese champions earlier this summer after one outstanding season in charge.

However, Chelsea's first choice to bolster the centre of their midfield remains Luka Modric and they are expected to shortly make an improved offer of £30m for the Croatian international.

Chelsea have not offered cash plus players -- the likes of Yossi Benayoun and Salomon Kalou have been mooted as makeweights -- for Modric, but Villas-Boas will certainly have to move on some of his foreign stars if he signs the players he is chasing in order to comply with the rules of Premier League 25-man squad sizes.

Chelsea have also lodged their interest in Spanish international Juan Mata, although they are yet to contact his club Valencia, who are prepared to sell the attacker for around £26m.

The 23-year-old had previously been a target for Arsenal but that deal stalled after the club failed to bid before a release clause expired.

Chelsea are believed to be planning to make three significant signings before the end of the month, which could involve spending at least £70m -- one left-sided player, one central midfielder and either a right-sided attacker or a striker.

Villas-Boas has carefully assessed the squad at his disposal, and having already acquired two other young players, Oriol Romeu and goalkeeper Thibault Courtois, for £12.2m in total, he wants to add more experience, creativity and pace.